1. Technical Field
The present invention relates to a mounting structure and a mounting method of a circuit board having a multi-layered ceramic capacitor thereon, and more particular, to a mounting structure of a circuit board having a multi-layered ceramic capacitor thereon capable of remarkably reducing vibration noise of the multi-layered ceramic capacitor by forming on a surface of the circuit board a land having the multi-layered ceramic capacitor mounted thereon and connecting the land with external electrode terminals of the multi-layered ceramic capacitor by a conductive material while setting a ration of a bonding area of the conductive material to be less than 1.4 as compared with an area of the external electrode terminal of the multi-layered ceramic capacitor.
2. Description of the Related Art
Generally, a multi-layered ceramic capacitor (MLCC) is a chip type capacitor that is mounted on a printed circuit board of various electronic products such as mobile communication terminals, notebooks, computers, personal digital assistants (PDAs), or the like, and plays an important role of charging or discharging electricity and has various sizes and stacked shapes according to usage and capacitance.
In addition, the multi-layered ceramic capacitor has a structure in which inner electrodes having different polarities are alternately stacked between a plurality of dielectric layers.
The multi-layered ceramic capacitor has been prevalently used as parts of various electronic devices due to advantages such as miniaturization, large capacitance, and easiness of mounting.
As a ceramic material forming a laminate of the multi-layered ceramic capacitor, a ferroelectric material such as barium titanate having a relatively higher dielectric constant is generally used. Since the ferroelectric material has piezoelectricity and electrostriction, when electric field is applied to the ferroelectric material, stress and mechanical deformation are shown as vibrations, which are transferred from the electrode terminal of the multi-layered ceramic capacitor to the board side.
That is, when AC voltage is applied to the multi-layered ceramic capacitor, stresses Fx, Fy, and Fz are applied to a main body of the multi-layered ceramic capacitor device in each direction of X, Y, and Z, which results in generating vibrations. The vibrations are transferred from the electrode terminal to the entire board which is an acoustic radiation surface, thereby generating noise, that is, vibrating sound.
The vibrating sound approximately corresponds to vibrating sound of an audible frequency (20 to 20,000 Hz) which may include a compass that gives a person an unpleasant feeling. Therefore, a need exists for a solution to the above problem.
Recently, in order to solve the problems due to the above-mentioned vibrating sound, various technologies, such as a technology of preventing vibrations due to an elastic deformation in the external terminal of the multi-layered ceramic capacitor, a technology of introducing separate parts for reducing generation of noise by suppressing propagation of vibrations generated due to piezoelectricity and electrostriction, a technology of forming board holes around the multi-layered ceramic capacitor mounted so as to suppress the vibrations of the board, or the like, has been disclosed, which require separate processes and are insufficient in a vibration prevention effect compared with the complexity of processes.
Meanwhile, as the multi-layered ceramic capacitor, there is a multi-layered ceramic capacitor having the substantially same width and thickness. In the case of the multi-layered ceramic capacitor having the substantially same width and thickness, when the multi-layered ceramic capacitor is mounted on the printed circuit board since directivity of inner conductors of the multi-layered ceramic capacitor cannot be recognized from the outside of the multi-layered ceramic capacitor, the multi-layered ceramic capacitors are mounted on the printed circuit board, regardless of the directivity of the inner conductors.
The differences in characteristics of the multi-layered ceramic capacitor are generated according to the direction of the inner conductors of the multi-layered ceramic capacitor mounted on the printed circuit board. In particular, the large difference in vibration noise characteristics due to the piezoelectricity of the multi-layered ceramic capacitor is shown.
In particular, it is found from the recent experiment results that the mounting direction of the multi-layered ceramic capacitor and the amount of a conductive material connecting the external electrode terminals of the multi-layered ceramic capacitor with the land are correlated with each other, which has a large effect on the vibration noise characteristics.
In particular, a need exists for a mounting structure and a mounting method capable of mounting the inner electrode surface of the multi-layered ceramic capacitor so as to be horizontal with the surface of the printed circuit board and remarkably reducing the vibration noises of the multi-layered ceramic capacitor by the ratio of the bonding area of the conductive material connecting the external electrode terminals of the multi-layered ceramic capacitor with the land to the external electrode terminal.